Non-small-cell lung carcinoma cells invade human bronchial mucosa in vitro

Two-dimensional vs. three-dimensional in vitro tumor migration and invasion assays

Motility and invasion are key hallmarks that distinguish benign from malignant tumors, enabling cells to cross tissue boundaries, disseminate in blood and lymph and establish metastases at distant sites. Similar properties are also utilized by activated endothelial cells during tumor-induced angiogenesis. It is now appreciated that these processes might provide a rich source of novel molecular targets with the potential for inhibitors to restrain both metastasis and neoangiogenesis. Such therapeutic strategies require assays that can rapidly and quantitatively measure cell movement and the ability to traverse physiological barriers. The need for high-throughput, however, must be balanced by assay designs that accommodate, as far as possible, the complexity of the in vivo tumor microenvironment. This chapter aims to give an overview of some commonly used migration and invasion assays to aid in the selection of a balanced portfolio of techniques for the rapid and accurate evaluation of novel therapeutic agents.

Tumor biology and experimental therapeutics

Recent research using multicellular tumor spheroids has resulted in new insights in the regulation of invasion and metastasis, angiogenesis and cell cycle kinetics. The onset and expansion of central necrosis in tumor spheroids has been characterized to be a complex interaction of several mechanisms; in a number of cases, necrosis is not a consequence of hypoxia or anoxia, but emerges as secondary necrosis following an accumulation of apoptosis in spheroids. Recent therapeutically oriented studies have been directed towards novel hypoxic markers, targeted therapy, multicellular-mediated drug resistance, and heavy ion irradiation of spheroids. Research efforts should be enhanced mainly in the fields of tumor tissue modeling by heterotypic three-dimensional (3D) cultures and of apoptotic versus necrotic cell death. Based on the fundamental differences between monolayer and 3D cultures, spheroids should become mandatory test systems in therapeutic screening programs.

Invasiveness by lacZ transfected non-small-cell lung cancer cells into human bronchial tissues in vitro

To facilitate the detection of invading tumor cells in a three dimensional coculture assay in vitro, the reporter gene Escherichia coli beta-galactosidase (lacZ), was transfected into a human large-cell lung carcinoma cell line GaL23. Multicellular spheroids initiated from the transfected cell line, GaL23LZ, were confronted with fragments of human bronchial tissue differing in their surface composition. While an intact surface epithelium was found to obstruct both adhesion and invasion of tumor cells, an exposed basal lamina augmented adhesion, migration and invasion of tumor cells into the normal tissue. Tumor cells, migrating on the surface of the bronchial fragments, were found to migrate between the epithelial cells and the basal lamina. Fibroblast covered stromal fragments, derived from resected non-small cell lung cancers, were found to be more edible to the invading tumor cells than subepithelial stromal fragments from normal bronchi. The lacZ transfection made it possible to quantitatively analyze the invasive process. While the transfection neither changed the invasive ability of the tumor cells in vitro or in vivo nor their growth pattern in monolayers, three dimensional growth represented by spheroid morphology and clonogenicity in soft agar was significantly changed. This model offers an in vitro system to study qualitative and quantitative aspects of tumor-host relationships in a complex microenvironment which has several similarities to the in vivo situation.